During front-end-of-line (FEOL) processing for CMOS microfabrication, electrode processing includes formation of self-aligned metallic silicides (also known as metallic salicides). In one such silicidation process, an alloy of Ni mixed with about 5 to 10% Pt (weight/weight) is deposited on a silicon substrate and subjected to thermal oxidation, causing the alloy to react with Si and form the silicide. The resulting Ni(Pt)Si demonstrates improved thermal stability as compared to NiSi alone.
To avoid bridging at spacers and isolation areas, after self-aligned silicidation is performed, unreacted NiPt and Pt residues must be removed. The post-salicidation clean process should optimally be selective so as to remove the residues without damaging exposed materials such as Si3N4 (spacers), SiO2 (field oxide), Ni(Pt)Si (contact and gate electrodes, and NiPtSiGe (contact electrodes of source/drain for strain applications).
Aqua regia, which is a solution of nitric acid and hydrochloric acid, is commonly used to remove unreacted NiPt and Pt residues from the substrate surface. However, as the concentration of Pt increases, aqua regia alone does not achieve complete removal of post-salicidation Pt residues due to temperature constraints during processing. Several other chemicals have been tested as a substitution for aqua regia, but none provides adequate cleaning performance without attacking TiN, SiN, and SiO2.
It is in this context that embodiments of the invention arise.